Polycarbonate diol is used as a material for reacting with an isocyanate compound to thereby produce a polyurethane. Polycarbonate diol is prepared by using diol components such as 1,4-butanediol, 1,5-pentanediol, 3-methyl-1,5-pentanediol, 1,6-hexanediol, 2-methyl-1,8-octanediol, 1,9-nonanediol and 1,4-cyclohexanedimethanol. It is known that a polycarbonate diol obtained from a diol of a chain aliphatic compound reacts with an isocyanate compound to thereby produce a flexible polyurethane which is excellent in water resistance, and that a polycarbonate diol obtained from cyclohexane dimethanol reacts with an isocyanate compound to produce a rigid polyurethane.
However, in polyurethanes obtained from these polycarbonate diols, flexibility and heat resistance are not well balanced and a flexible polyurethane has a poor heat resistance while a rigid polyurethane, which has a heat resistance, not only has a defect of poor flexibility, but also involves a disadvantage of low reliability in long-term insulating performance due to its high hygroscopic property under high temperature/high humidity conditions since it contains a high proportion of urethane bonds.